The most common and most likely answer to this crossword clue is the 8 letter word UNBOLTED
U
N
B
O
L
T
E
D
Buddy explains!

The straight part
We know that "left open" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case left open = unbolted.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNBOLTED mean?
UNBOLTED verb- To unlock by undoing the bolts of.
- Not fastened with a bolt.
- Not sifted.
- Coarse, uncultured, vulgar.